Reindeer eyes change color in winter

A new study finds that reindeer eye color changes with the seasons.

Quick – what color are a reindeer's eyes? If you said, “blue,” you are correct. If you said, “gold,” you are also correct. Turns out that reindeer have eyes that change color with the seasons – the only mammals known to do so.

Biologists at the UK’s University College London and Norway's University of Tromsø made the discovery, described in the journal Proceedings of the Royal Society B: Biological Sciences published Wednesday.

It’s actually a reflective layer at the back of a reindeer’s eyeballs that changes color in response to seasonal differences in light.

In the summer, the reflective layer is gold, and in winter it’s blue.

"We have some evidence that the blue reflection in winter amplifies ultraviolet light, while in summer it suppresses it," lead researcher Professor Glen Jeffery from UCL said.

The blue color helps reindeer see during the 24 hours of darkness in the Arctic winter. "This gives them an advantage when it comes to spotting predators, which could save their lives,” Jeffery said.